October 2013 - Practical Welding Letter - Issue No.122

Important Notice

The Mid September 2013 Issue of Practical
Welding Letter, Bulletin 89, introducing Online Resources on Duplex Stainless Steels was distributed by e-mail. It is available at PWL#121B - Bulletin 89 and from the Welding Resources Page.

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This October 2013 Issue No. 122 of Practical Welding Letter begins with one more article on Duplex Stainless Steels. At the initiative of a kind Reader who suggested to add a few details on welding procedure qualification, we asked the original Author, Naddir M Patel to comment on the recommendation.

Interested readers could download the three files in a single folder, to get a great reference at their fingertips. The Author added, in his letter, the following observation: "A concern that many fabricators have though, is the ready availability of DSS as opposed to 316 or 304. I wonder if a manufacturer could be requested to address this situation." Maybe other readers could comment on this concern from their experience.

We then report on an article that addresses Aluminum Welding Safety Tips, a most painful subject if the precautionary requirements are carelessly dismissed as not important.

Hydrogen control should be addressed always, especially when
welding high strength steels. An article is reported that summarizes the most important precautions in five simple steps that should become the habit for those who work regularly with those materials.

Integrated Computational Materials Engineering is recently becoming a most useful tool for simulating optimized results, before dealing with real materials and processes. When confronted with new challenges one should be alerted to the capabilities and to the results already achieved by these methods.

Two articles on practical applications of the new techniques are referred to. One deals with designing new materials to display specific properties, the other with optimizing a complex heat treatment process to minimize distortions.

Fine tuning welding parameters by remote control may increase productivity, improve quality and welders safety by avoiding their falling in a cluttered up fabrication environment, if
their displacements are reduced.

Implementing the required technology is recommended for industrial sites where many welders work on their assignments in close proximity to one another in busy surroundings. Readers may wish to explore more in depth the issues involved.

For site updating we revised two related pages, one on Friction Welding Processes, the other on Friction Stir Welding Equipment, hoping to help interested readers in finding the information they seek.

The other sections follow as usual, to be found where they are expected. Readers looking for information are urged to browse the Site Map page or to type the keywords of their query in the search box appearing on almost every page of this website.

Readers who know what they are talking about are invited to ask their questions by giving full details of their problems. (We got many examples of unaware
inquirers, too lazy to clarify their own questions.)

We hope you will enjoy reading, while at the same time getting updates on some useful subjects. Comments and feedback are welcomed. DON'T USE REPLY. Fill instead the Contact Us Form.

Thank you for the very informative article on duplex stainless steels.

[The article Duplex Stainless Steels - Best Practices for Selection and Welding was published (2) in Issue 121 of Practical Welding Letter for September 2003. Click on PWL#121 to see it.
Bulletin 89, listing Online References to Duplex Stainless Steels (DSS), is available at PWL#121B - Bulletin 89.
]

I have a suggestion regarding welding procedure qualification.

In addition to Charpy specimens, I would also encourage having a set of micrograph samples made by a metallurgical lab to verify the austenite/ferrite balance in the weld metal
and HAZ has been achieved.
I have found that interested parties reviewing our qualifications to weld duplex stainless are usually happy to see
we have an additional verification step built-in to our procedures.

Thanks for the feedback. I had not suggested the requirement for microstructure analysis because that is standard procedures suggested in API technical report 938C.

API TR 938-CUse of Duplex Stainless Steels in the Oil Refining Industry
Second Edition, standard published 04/01/2011 by American Petroleum Institute

As such, a reference to this API specification in the follow up note to the article would definitely give good information to a reader new to DSS.
The following information is a summary of API 938C requirements.
Keep in mind that these specs are North American oriented as ISO & EN are generally not
referenced here.

Additional Testing:Ferrite Determination: The PQR should include a metallographic characterization of the microstructure of the weld according to ASTM A923 - 08Standard Test Methods for Detecting Detrimental Intermetallic Phase in Duplex Austenitic/Ferritic Stainless Steels, method A.
The etchant used shall enable ferrite, austenite and any sigma phase to be clearly identified. The microstructure should confirm the presence of grain boundaries without any continuous precipitates. The sigma phase shall not exceed 0.5%. The intermetallic phases, nitrides and carbides shall not exceed 1.0% in total.

The ferrite content of the weld and parent metal shall be determined by the point counting method detailed in ASTM E562 - 11Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count.

A standard 25 points grid will be applied at a 400X, magnification for
the weld and 700X minimum for the Heat Affected Zone (HAZ).
The following locations are recommended for testing.

Parent Metal: One measurement on both sides of the weld at mid thickness. (Total 2)

HAZ: On each side of the weld in the region of the root pass.
Sufficient micrographs may be required due the narrow HAZ.

Weld Metal: Three measurements near to the vertical center-line of the weld, one in the cap, one in the root and one at mid-thickness. (Total 3)

Cross referencing to be carried out by the same electromagnetic measurement devise (EMD) planned for use on production welds.
The acceptable range for ferrite is 35 to 55% throughout the weld area, preferably at the lower side of this range.

A ferrite count will be carried out on production welds to verify the % ferrite within the control limits set in the Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR).

Production
ferrite testing should be performed ideally with a Fischer Feritscope or equivalent EMD that can measure both FN (ferrite numbers) and % ferrite.

The production testing is to be performed at intervals of 3 tests every 5 feet of weld; one in each of the base metal and weld. Whereas the acceptable range for ferrite is 35 to 55%, preferably at the lower side of this range, all single point measurements should be within the range specified on the PQR.

[Note: We reported in PWL#119, section 3, on a study that questioned the interlaboratory correlation of results obtained by metallographic methods, and recommended that "Ferrite requirements for weld metals should be based as much as possible upon measurement of FN by instruments calibrated according to the ISO 8249 or AWS A4.2 standards".

The suitability of
metallographic analysis results for validation of welded microstructures, implies that the reported variability does not modify the conclusions, due to the acceptable wide range for ferrite (35 to 55% throughout the weld area). Confirmation should be sought by interested parties.]

Corrosion Testing: ASTM G48 - 11Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride
Solution
corrosion testing, as an integral part of the welding procedure is required. The test may not model the exact service corrosion environment, but gives a good qualitative assessment of the welds general corrosion resistance. This gives a good indication that the welding method is satisfactory. G48 test temperature for standard duplex is typically 22°C, and for super duplex is 35°C.

In production, hardness traverse should sample the HAZ and the weld metal. Hardness conversions to be referenced from API-938C, figure 2. For sour service hardness values should comply with NACE MR0175 (ANSI/NACE MR0175/ISO 15156, Petroleum and natural gas industries—Materials for use in H2S-
containing environments in oil and gas production).

Good impact test results are also a good indication of a successful welding procedure. A production test plate for impact testing is good practice. Associated with the minimum design temperatures and engineering recommendations, minimum CVN (Charpy V-notch Number, the output of a Charpy impact test) of the parent and weld metal should be 45J @ -46°C as per ASTM A923 method B. Two sets, each three specimen should ideally be carried out with notch located in weld metal and fusion line respectively.The HAZ being very narrow, testing in this segment is not feasible.

PMI:
Positive Material Identification either by X-ray
Fluorescence (XRF) or by Optical Emission Spectroscopy (OES) to be carried out on all production welds. The report should include Cr, Mo, Si, W, Ti, Nb, C, O, N Ni, Mn and Cu.

A good description of these 2 PMI procedures is available at
http://www.pyromation.com/TechInfo/WhitePapers/PMI_Comparing_Two_Test_Methods.aspx

3 - How to do it well: Aluminum Welding Safety Tips

While safety practices risk to be dismissed and neglected by busy welders, it is essential that they be studied and rehearsed at regular intervals by all involved, and be enforced by management.

This is important both at the single individual level, for the responsibility one has for proper self well being (including one's family) and
at the working place, where accidents should not be tolerated.

An Article titled as this note was published at page 34 of the September 2013 issue of the Welding Journal. It should be studied thoroughly by all involved, by dedicating sufficient attention to each precaution and by translating each recommendation in action items to be implemented as required.

The article singles out specific considerations affecting aluminum welding. In particular the following areas are dealt with in detail: Hot Metal Burns, Electrical Shock and Radiated Light.

To avoid the described painful consequences of these hazards, one should be aware of the dangers of careless behavior, and one should make a habit of using the prescribed personal protective equipment.

Additional factors to keep in mind are excessive Noise, Fume Emissions, Cleaning Fluids and Explosions, to be taken care of with suitable attention.

Serious reading of the original article in
the magazine quoted above is recommended to all involved with aluminum welding. Safety in the workplace is imperative.

Precautions are never excessive. Avoidable accidents should never occur.

4 - Filler Metal Care for Hydrogen Control

An Article published at page 82 in the September 2013 issue of the Welding Journal summarizes the risks posed by hydrogen finding its way in the weld pool, especially in high strength steels.

A short introduction reminds of the destructive dangers looming on welding production, if inadequate care is exerted to prevent absorption of this light gas in the molten metal, where it can easily diffuse.

Five practical steps are then suggested to implement methods to control hydrogen diffusion in the welding
process.

The first, to minimize joint stress, is a requirement of any good design, and beyond the reach of the welder. Anyhow a diligent welder who remembers past successes and failures may be able to provide useful hints to a careless engineer who overlooked dangerous details.

The second is the reminder of the importance of careful application of well conceived welding procedures, with reference to adequate thermal cycles before and after welding.

The third, considering the selection of suitable filler metals, may be imposed on the welder from above, even by an over conscious purchasing agent willing to spare a few pennies in consumables. The recommendations of an experienced welder may be invaluable to the organization, if due attention is paid to the consequences of improper selection.

Suitable storing and handling of filler metal is certainly in the welder's hands and under his/her responsibility.
Prevention of moisture absorbency is
of utmost importance, as good welders should know. The application of baking cycles should be thorough and adequate, not too difficult to take care of.

Assuring suitable condition of consumable packaging at all times should become most natural to all.

Making sure that anyone involved in fabrication is aware of the catastrophic consequences of hydrogen induced cracking, can be a necessary condition to take always utmost care of hydrogen prevention in all phases of welding.

Readers are invited to seek and read the original article mentioned above.

Infrared
radiation is that part of the electromagnetic energy spectrum with wavelengh between 770 and 12000 nanometers.

Laser beam oxygen cutting is a variation using heat from a laser beam to cut metal.

Oxygen arc cutting is a process that uses an arc between the workpiece and a consumable tubular electrode through which oxygen is blown to the workpiece to cut into the metal.

Pulse time in resistance welding is the duration of a current pulse.

Root pass is a weld pass made to produce a root bead.

Synchronous timing in resistance welding, is the initiation of each half cycle of welding transformer primary current on an accurately timed delay relative tothe polarity reversal of the powewr supply.

Thermite mold is formed around the workpiece joint to receive and shape the molten metal.

Workpiece lead is the electrical conductor between the welding current source and the
workpiece connection.

7 - Article: Integrated Computational Materials Engineering (ICME)

Technological Experience is an important asset developed through a long and successful professional career. Those who were determined to achieve a substantial level of competency in their field are rightfully recognized as fundamental pillars in their organizations and enjoy the coveted status of mentors and leaders.

In times of accelerated development however, it is essential to recognize that new techniques become available. Managers and Engineers should be alerted that significant progress has been achieved quite recently in a branch of Materials Engineering relying heavily on recently developed Computational methods.

While
the practical applications are quite specialized and require long and thorough preparation to learn and use the new tools available, the decisions to dedicate efforts toward specific applications rest with informed managers who should know which advantages could be reaped by developing suitable complex problem solving routines.

Two articles published in the September issue of Advanced Materials and Progress, an ASM International magazine,
highlight some of the uses and results recently implemented.

At page 17 the first article explains how this versatile tool is instrumental in drastically reducing the development time of new materials for aerospace applications.

By using ICME tools these new alloys are obtained not only faster, but also can be designed much more inexpensively, to meet specific property targets such as strength, toughness, corrosion resistance, and others.

Property targets are established in the design stage by specifying and developing precise chemical composition and processing parameters.

Using grants and support generated by specific US government initiatives to promote projects, originating by several Departments and Science Research institutions, a private company undertook to develop entirely new alloys to solve
serious materials-related problems.

The article describes, without much detail, how proprietary thermodynamic and kinetic databases provide the data that feed into precipitation prediction and microstructural evolution models. These are used to adjust chemistry
and thermal processing parameters that help predict equilibrium phases needed to provide the sought properties.

Obviously the initial specifications must be fine-tuned by practical
experimentation, but the outcome is generally improved performance at much reduced development costs.

The article lists several different new alloys developed to achieve specific target requirements, in particular four ultrahigh performance steels. The time span of five to eight years from development to production and field testing is considered a remarkable achievement.

Given the proven successes realized by using ICME in the last 15 years, there is well founded expectation that the future integrated computational design of novel materials will impact industry, as both demand and successful implementation of advanced ICME-designed alloys grows.

It explains how the need to predict heat transfer during high pressure gas quenching and to couple it with phase transformation distortion analysis, led to the development of a special Computational program, called ICME-GearHT. The capability of this model, that incorporates even latent heat release due to phase transformation, was validated using experimental data.

Practical experimentation including temperature measurements at different fan speeds permits to validate the model predictions with actual results. The model was used to evaluate properties of furnace-fixture materials, chamber configurations,
and parts loading in the furnace.

Distortion calculations are compared with experimental results. The model can be used to identify the best effective heat treatment solutions for minimized distortion and to provide guidelines for process design and optimization.

Recent experimental studies have shown that use of carbon-fiber composite (CFC) fixtures reduces distortion
by 25%, and by 50% if combined with step quench.

Readers involved with research of improved materials for special applications or with gear deformation problems following heat treatment might consider looking deeper into the issues described to benefit from these advanced technological development. All readers are invited to seek the quoted articles.

Process
Optimization

[From Pollock Research Group - Materials Department - College of Engineering - UCSB
University of California - Santa Barbara] at
https://www.engr.ucsb.edu/~pollockgroup/?p=projects

The two reviewed and updated Pages of this Month in our website (www.welding-advisers.com) deal with related
processes. The first page concentrates on friction processes, which were developed also for unique repair applications of costly items like the main shaft of gas turbine engines.

The other page gives a short story with references of the innovative process which enjoyed successful applications in most demanding fields like aerospace. It also points to a few reference links for further information. It is found at Friction Stir Welding Equipment.

Readers can browse the Site Map for main subject pages, the Welding Topics page for the titles of
main PWL Articles, and the Welding Resources page for lists of Online Links to rich sources of knowledge.

Comments, questions and feedback are welcomed. Use the Contact Us Form.

9 - Short Items

Do you know...

...that 238,000 new welders will be needed by 2019?
Sorry! Link removed by the Source masslive

...how to make a New Welding Engineer?
Sorry! The link was removed by the Source AWS.

...where to find an
intensive two-day course on resistance welding?RWMA.

9.1 - Abrasive Wear is the removal of material from a surface by hard particles sliding or rolling across the surface under pressure.

9.2 - Ball Milling is a method of grinding and mixing material, with or without liquid, in a rotating cylinder or conical mill partially filled with
grinding media such as balls or pebbles.

9.3 - Canning is enclosing a highly reactive metal preform within a can of relatively inert material for the purpose of hot working without undue oxidation of the active metal.

9.4 - Deep Drawing is forming deeply recessed parts by forcing sheet metal to undergo plastic flow between punch and dies, usually without substantial thinning of the sheet.

9.5 - Electrochemical Reaction is caused by passage of an electric current through a medium that contains mobile ions (as in electrolysis); or, a spontaneous reaction made to cause current to flow in a conductor external to this medium (as in a galvanic cell). In either event, electrical connection is made to the external portion of the circuit via a pair of electrodes.

9.6 - File Hardness is determined by the use of a steel file of standardized hardness on the assumption that a material that cannot be cut with the file is as
hard as, or harder than, the file. Files covering a range of hardnesses may be employed; the most common are files heat treated to approximately 67 to 70 HRC.

An article published in the September 2013 issue of the Welding Journal at page 44, makes the point that implementing remote control for welding equipment has distinctive advantages.

Wireless commands permit continuous control of welding parameters and shutoff switch operation without leaving the weld location, while eliminating additional cords and control cables cluttering
the working space.

In construction places power sources may be quite far from the welder. Remote controls avoid needless displacements of welders, involving danger of falls, while removing the control cable tripping hazard.

Such controls are available for SMAW (Shielded Metal Arc Welding) and GTAW (Gas Tungsten Arc Welding) as well as for GMAW (Gas Metal Arc Welding) and FCAW (Flux Cored Arc Welding).

Wireless remote controls typically operate within line of sight between command and power source. Other remote controls relate signals through the welding cables, eliminating additional control cables, and solving the line of sight issue.

As many job sites have multiple power sources in one area, full control tracks cables back to the correct power source eliminating possible errors, and it helps improve productivity and quality.

Error messages can be transmitted, alerting the welder of incorrect
polarity. Information to be transmitted back and forth includes the same details available on the power source itself and on the wire feeder.

Processes controllable from a distance include modified short circuit GMAW and Pulsed GMAW. Full remote control capabilities, process selection, material type, and wire diameter, gas type, wire feed speed, and voltage need connection of the power source with a specially designed "smart" wire feeder.

This type assures that the waveform selected extends to the point of use in an optimal state because it is only traveling the length of the GMAW torch cable.

Safety, productivity and quality are powerful incentives recommending the adoption of this advanced remote control welding technology wherever the sheer number of power sources active at the same time in the same place may be cause for confusion and errors.

Readers are urged to seek the original article in the magazine
pointed at above.

Could anyone find a better example of a query whose enquirer has no idea of the subject?

13.2 - An unfortunately recurring pattern:

A reader sends a question.
I do my best to give a sensible answer. If the data are not sufficient, I write that much.
Obviously the recipient is not satisfied. Probably for that reason I get no further acknowledgement.I still ignore the real cause for the interruption.

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